This invention relates to optical somato-measuring apparatus that draws information about the internal tissues of a living body, such as the intravascular bloodstream velocity, using laser beams.
Various apparatus obtain information about the internal tissues of an object by throwing a beam of light on the object and measuring the light scattered by the internal tissue. These apparatus require a light source that supplies a beam of light to the object and a photometer to measure the light scattered therefrom. Ordinarily, the light source and photometer are disposed on the same side. This arrangement is known as the reflection type. In the reflection type apparatus, however, the photometer receives a strong light reflected from the surface of the object, along with the scattered light from the internal tissue thereof that is to be measured. Accordingly, it becomes very difficult to make accurate measurement of the scattered light from the internal tissue.
Laser microscopes and other similar modern optical apparatus are in practical use. As this type of optical measurements are increasing, such apparatus will find increasingly wide application. But they also encounter the aforesaid problem of reflection from the object surface. That is, the measuring device cannot accurately measure the scattered light, receiving the surface-reflected light that has nothing to do with the minute tissues inside the object.
Now an application to the laser Doppler microscope will be described. First, a beam of light, 10 to 40 .mu.m, emitted from a laser is divided into two light-beams, using a prism etc. The two light-beams are intersectingly thrown on, for example, a minute blood vessel in a living tissue through an optical system comprising a set of microscope lenses. Blood cells in the blood vessel scatter the thrown light-beams. Consequently, the two incident lights cause Doppler deviations according to their respective incident angles and the flow rate of the blood cells, whereby the frequency of the lights is slightly changed. By measuring the lights scattered by the blood cells with a photomultiplier incorporated in the microscope, information corresponding to the bloodstream velocity is obtained. If the microscope is focused on a point where the two laser beams intersect, the beat frequency of the two Doppler-deviated lights is taken out in the form of an electric signal. This frequency theoretically is proportional to the bloodstream velocity in the minute blood vessel.